The present invention relates to phenyl-linked polybenzoxazoles having terminal, aryl- or heteroaryl-attached cyanate groups which can be used for adhesive bonding and as dielectrics, especially for electronic components, and to a process for preparing them.
There is a need in microelectronics for highly heat-stable polymers as protective coats and insulating coats. Accordingly, these polymers can be used as dielectrics between two metal tracks and/or metal planes, in the case, for example, of multichip modules, memory chips and logic chips, or as a buffer coat (Buffer code) between the chip and its housing.
Some of these polymers, such as precursors of aromatic polyimides (PI) or polybenzoxazoles (PBO), exhibit good solubility in organic solvents and also good film-forming properties and can be applied to the electronic components by means of inexpensive control technology. Following a temperature treatment, such precursors are transformed or cyclized to give the PI or PBO (see scheme for PBO below in this respect) and so acquire their ultimate properties. An alternative is to prepare these polymers in cyclized form already, although the solubility of these ready-cyclized polymers is reduced.
Scheme: 
In the course of the cyclization, water is liberated. Normally, this does not give rise to any problems as far as the application is concerned. For particular applications, however, this may be problematic if the water finds it very difficult or impossible to escape by diffusion. The consequence is blistering or cracking.
In chip technology it is necessary, for example, to fill very narrow trenches between the metallic conductor tracks with an insulator, the dielectric. The aspect ratios (ratio of feature height to feature width) may be well over 4, with the width of the trenches being, for example, only 100 nm. In such cases materials are needed which not only exhibit a good insulating effect but also exhibit very good adhesion and filling properties. In this context, adhesion both to the sidewalls and to the base is important. No water must be liberated, by cyclization, for example, since in these cases the water is virtually unable to escape by diffusion, and produces blisters. A chemical reaction which lowers the solubility of the material and ensures that the ultimate properties are obtained (crosslinking or cyclization) must not then include any elimination of any constituents whatsoever.
For use in microelectronics, the materials must also withstand operating temperatures up to 450xc2x0 C. or more without problems and must be stable toward process chemicals, such as solvents, strippers (solvents or substances for removing photoresists), bases, acids or aggressive gases.
One objective of the present invention is to provide novel insulating polymers (dielectrics) which combine good electrical insulation and sufficient temperature stability with very good adhesive and filling properties and which do not give off any constituents on crosslinking.
The state of the art has attempted to solve these problems by means, for example, of benzocyclobutenes (Dow Chemical, ref.: H. W. Boone, D. W. Smith, D. A. Babb, Polymer Preprints Vol. 39, No. 2, p. 812f.), which were also employed in microelectronics. These materials, however, do not exhibit sufficient adhesion and are not sufficiently temperature-stable. DE 44 32 965 C1 disclosed polycyanurate materials which can be used for adhesive bonding. The adhesiveness of these materials, however, is not sufficient for many adhesive applications, especially in the manufacture of electronic components.
The present invention accordingly provides, according to claim 1, phenyl-linked polybenzoxazoles which contain terminal, aryl- or heteroaryl-attached cyanate groups.
Provided in particular are inventive polybenzoxazoles of the following general formula (I): 
where for a, axe2x80x2, axe2x80x3, b, bxe2x80x2 and bxe2x80x3 independently of one another it is the case that:
a, axe2x80x2, axe2x80x3=0-100;
b, bxe2x80x2, bxe2x80x3=0-100;
X has the following definition: substituted or unsubstituted aryl, a substituted or unsubstituted polynuclear aromatic hydrocarbon compound, a substituted or unsubstituted fused ring system or a substituted or unsubstituted heterocyclic radical;
Y1 and Y2 have the following definition, it being possible for Y1 to be the same as or not the same as Y2:
substituted or unsubstituted aryl, a substituted or unsubstituted polynuclear aromatic hydrocarbon compound, a substituted or unsubstituted fused ring system, or alkyl, alkenyl, alkynyl, aralkyl, aralkenyl, aralkynyl, heterocyclo or cycloalkenyl, each substituted or unsubstituted;
and Z1 to Z3 each independently of one another have the following definition:
aryl, aralkyl, aralkenyl, aralkynyl, heteroaryl, each substituted or unsubstituted, a substituted or unsubstituted polynuclear aromatic hydrocarbon compound or a substituted or unsubstituted fused ring system.
The present invention further relates to a process for preparing polybenzoxazoles of the general formula (I), comprising the following steps:
a. reacting a bisaminophenol of the formula H2Nxe2x80x94(HO)Z1(OH)xe2x80x94NH2 and/or H2Nxe2x80x94(HO)Z2(OH)xe2x80x94NH2 and/or H2Nxe2x80x94(HO)Z3(OH)xe2x80x94NH2 with benzene-1,3,5-tricarboxylic acid, then optionally with a compound for introducing the group Y1 and/or Y2, and then with a compound for introducing the group Xxe2x80x94OH, to give a phenyl-linked polybenzoxazole having terminal, aryl- or heteroaryl-attached hydroxyl groups;
b. reacting the phenyl-linked polybenzoxazoles obtained in step a. and containing terminal, aryl- or heteroaryl-attached hydroxyl groups with cyanogen bromide to give phenyl-linked polybenzoxazoles having terminal, aryl- or heteroaryl-attached cyanate groups;
Z1, Z2, Z3, X, Y1 and Y2 being as defined above.
The present invention further relates to the use of polybenzoxazoles of the general formula (I) as dielectrics in electronic components and for adhesive bonding.
The present invention relates to phenyl-linked polybenzoxazoles having terminal, aryl- or heteroaryl-attached cyanate groups, especially polybenzoxazole cyanates of the above-indicated formula (I).
It is preferred if a, axe2x80x2 and/or axe2x80x3 in the formula (I) independently of one another are 0-20, more preferably 1-20, and/or b, bxe2x80x2 and/or bxe2x80x3 independently of one another are 0-20, more preferably 1-20.
Particular preference is further given to:
compounds where X has the following definition: 
where Q is: xe2x80x94Oxe2x80x94, Sxe2x80x94 or xe2x80x94NHxe2x80x94;
R1 is: xe2x80x94H, xe2x80x94CF3, xe2x80x94OCN, alkyl or aryl;
R2 is: xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NR3xe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94S2xe2x80x94, xe2x80x94CH2xe2x80x94, and also: 
R3 is: xe2x80x94H, and also:
xe2x80x94(CH2)kxe2x80x94CH3 (k=0-10) xe2x80x94(CF2)kxe2x80x94CF3 (k=0-10) 
and R4 is: alkyl having from 1 to 10 carbon atoms or aryl.
Preference is further given in accordance with the invention to polybenzoxazoles of the formula (I) having terminal, aryl- or heteroaryl-attached cyanate groups wherein Y1 and Y2, where Y1 can be the same as or not the same as Y2, are: 
where R1, R2, R3 and Q are as defined above.
Preference is additionally given in accordance with the invention to polybenzoxazoles having terminal, aryl- or heteroaryl-attached cyanate groups of the formula (I) wherein Z1, Z2 and Z3, it being possible for Z1 to Z3 to be the same as or not the same as one-another, are: 
where Q and R2 are as defined above 5 [sic].
In the definition of Y1 and Y2, suitable examples of polynuclear aromatic hydrocarbon radicals are fused ring systems and heterocyclic compounds: biphenyl, anthracene, naphthalene, fluorene, pyrene, thiophene, thiazole or benzothiazole, imidazole or benzimidazole, pyrrole, furan, pyridine or pyrazine or derivatives thereof.
Suitable examples of polynuclear aromatic hydrocarbon radicals, fused ring systems, and heterocyclic compounds for Z1 to Z3 are biphenyl, anthracene, anthraquinone, fluorene, pyrene, thiophene, thiazole or benzothiazole, imidazole or benzimidazole, pyrrole, furan, pyridine, pyrazine or derivatives thereof.
Particularly preferred radicals for Z1 and/or Z2, and/or Z3, are: 
Particularly preferred radicals for Y1 and/or Y2 are: 
Particularly preferred radicals for X are: 
In accordance with the invention, the oxazole cyanates of the formula (I) can be prepared in two steps:
a. reacting bisaminophenol of the formula H2Nxe2x80x94(HO)Z1(OH)xe2x80x94NH2 and/or H2Nxe2x80x94(HO)Z2(OH)xe2x80x94NH2 and/or H2Nxe2x80x94(HO)Z3(OH)xe2x80x94NH2 with benzene-1,3,5-tricarboxylic acid, then optionally with a compound for introducing the group Y1 and/or Y2, and then with a compound for introducing the group Xxe2x80x94OH, to give a phenyl-linked polybenzoxazole having terminal, aryl- or heteroaryl-attached hydroxyl groups;
b. reacting the phenyl-linked polybenzoxazoles obtained in step a. and containing terminal, aryl- or heteroaryl-attached hydroxyl groups with cyanogen bromide to give phenyl-linked polybenzoxazoles having terminal, aryl- or heteroaryl-attached cyanate groups.
On Step a:
This reaction can be performed in a variety of ways in accordance with the invention.
In accordance with the invention, for example, the compound for introducing the group Y1 and/or Y2 is preferably a dicarboxylic acid of the formula HOOCxe2x80x94Y1xe2x80x94COOH and/or HOOCxe2x80x94Y2xe2x80x94COOH, the compound for introducing the group X is preferably a hydroxy carboxylic acid of the formula HOxe2x80x94Xxe2x80x94COOH, and the reaction of step a. takes place in the presence of phosphorus pentoxide. This leads directly to the formation of a cyclized, phenyl-linked polybenzoxazole containing aryl- or heteroaryl-attached hydroxyl end groups.
In this reaction the hydroxyl group of the hydroxy carboxylic acid is preferably protected in order to prevent side reactions. Examples of suitable protected groups are alkyl groups, e.g., tert-butyl, alkylcarbonyl groups, preferably acetyl groups, benzoyl groups or alkylbenzoyl groups. The removal of the protective group to give polybenzoxazoles containing aryl- or heteroaryl-attached hydroxyl end groups takes place in accordance with known techniques. For example, an alkylcarbonyl protective group, such as the acetyl group, can be eliminated in dimethylformamide and ammonia. In the case of an alkyl protective group, the elimination can be accomplished by means of a strong acid such as hydrobromic acid, for example.
Examples of preferred solvents for the first reaction step include methanesulfonic acid, N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide, xcex3-butyrolactone, polyphosphoric acid, a mixture of sulfuric acid and phosphoric acid, and mixtures of these solvents. In the case of this variant of the process, the solvent is in a mixture with phosphorus pentoxide, preferably with 5-10% by weight of phosphorus pentoxide, more preferably 7-8% by weight, based on the composition comprising solvent and phosphorus pentoxide.
Particular preference is given to a mixture of methanesulfonic acid and phosphorus pentoxide, preferably having a phosphorus pentoxide content of 5-10% by weight, more preferably 7-7.5% by weight.
In accordance with the invention, the reaction temperatures in step 1 are preferably between 50 and 150xc2x0 C., the reaction times being between 1 hour and 20 hours, with from 4 hours to 12 hours being preferred.
The resulting polymer can be precipitated by dropwise addition of the reaction solution to a precipitating medium, followed by washing and drying. Suitable precipitating media are water, alcohols, such as isopropanol, butanol or ethanol, and mixtures of these precipitating media. The precipitating medium may preferably also contain up to 10% ammonia.
A further possibility for the reaction in accordance with the first reaction step is the reaction of a bis-o-aminophenol with benzene-1,3,5-tricarboxylic acid and then with a dicarboxylic acid and a hydroxy carboxylic acid in the presence of a carboxylic-acid-activating compound, such as carbonyldiimidazole or dicyclohexylcarbodiimide or hydroxysuccinimide or hydroxybenzotriazole, for example. In this case the compound for introducing the group Y1 and/or Y2 is a dicarboxylic acid of the formula HOOCxe2x80x94Y1-COOH and/or HOOCxe2x80x94Y2-COOH, the compound for introducing the group X is a hydroxy carboxylic acid of the formula HOxe2x80x94Xxe2x80x94COOH, and the reaction of step a. takes place in the presence of a carboxylic-acid-activating group.
Solvents which can be used were again the solvents mentioned above for step a., but without the presence of phosphorus pentoxide.
In the case of this reaction the hydroxyl group of the hydroxy carboxylic acid is preferably protected in order to prevent side reactions. Suitable protective groups are, for example, alkyl groups, e.g., tert-butyl groups, alkylcarbonyl groups, preferably acetyl groups, benzoyl groups or alkylbenzoyl groups. The removal of the protective group to give phenyl-linked polybenzoxazoles containing aryl- or heteroaryl-attached hydroxyl end groups takes place in accordance with known techniques.
Thereafter the product can be cyclized in solution to give the polybenzoxazole having terminal, aryl- or heteroaryl-attached, hydroxyl groups. This is done preferably in the presence of a catalytic amount of acid by means of temperature treatment at a temperature of preferably from 150 to 200xc2x0 C.
Suitable in principle are all reagents which per se bind the water formed during the reaction or which raise the reactivity of the carbonyl group. Preference is given, however, to the abovementioned compounds carbonyldiimidazole or dicyclohexylcarbodiimide or hydroxysuccinimide or hydroxybenzotriazole. The resulting polymer can be precipitated by adding the reaction solution dropwise to a suitable precipitating medium and then drying it. Suitable precipitating media are water, alcohols, such as isopropanol, butanol or ethanol, and mixtures of these precipitating media. The precipitating medium may preferably also include up to 10% of ammonia.
A further possibility for reaction in accordance with the first reaction step is the reaction of a bis-o-aminophenol with benzene-1,3,5-tricarbonyl trichloride and then with a dicarbonyl dichloride and a hydroxy carbonyl chloride in the presence of a base, such as pyridine, morpholine, pyrrole or triethylamine, for example.
In this case in step a. the compound for introducing the group Y1 and/or Y2 is a dicarbonyl chloride of the formula ClOCxe2x80x94Y1xe2x80x94COCl and/or ClOCxe2x80x94Y2xe2x80x94COCl or another reactive dicarboxylic acid derivative. xe2x80x9cReactive dicarboxylic acid derivativexe2x80x9d means that the carbonyl groups have a higher carbonyl-group reactivity in comparison to the carboxylic acid. The compound for introducing the group X is a hydroxy carbonyl chloride of the formula HOxe2x80x94Xxe2x80x94COCl or another reactive hydroxy carboxylic acid derivative. Step a. is conducted in the presence of an N-containing organic base.
Solvents which can be used are again the solvents mentioned above for step a., but without the presence of phosphorus pentoxide.
In the case of this reaction the hydroxyl group of the hydroxy carboxylic acid is preferably protected in order to prevent side reactions. Suitable protective groups are, for example, alkyl groups, e.g., tert-butyl groups, alkylcarbonyl groups, preferably acetyl groups, benzoyl groups or alkylbenzoyl groups. The removal of the protective group to give phenyl-linked polybenzoxazoles containing aryl- or heteroaryl-attached hydroxyl end groups takes place in accordance with known techniques.
Thereafter the product can be cyclized in solution to give the polybenzoxazole having terminal, aryl- or heteroaryl-attached, hydroxyl groups. This is done preferably in the presence of a catalytic amount of acid by means of temperature treatment at a temperature of preferably from 150 to 200xc2x0 C.
The resulting polymer can be precipitated by adding the reaction solution dropwise to a suitable precipitating medium and then drying it. Suitable precipitating media are water, alcohols, such as isopropanol, butanol or ethanol, and mixtures of these precipitating media. The precipitating medium may preferably also include up to 10% of ammonia.
On Step b:
The second step in the process for preparing polybenzoxazole cyanates of the general formula (I) consists in reacting the phenyl-linked polybenzoxazoles obtained in step 1, containing terminal hydroxyl groups, with cyanogen bromide to give phenyl-linked polybenzoxazoles having terminal cyanate groups. In this case the dried polybenzoxazole having hydroxyaryl or hydroxyheteroaryl end groups can be reacted with cyanogen bromide in a suitable solvent, preferably in the presence of a base. After the end of the reaction the product can be precipitated from a precipitating medium, washed and dried. Suitable precipitating media are preferably aprotic solvents, such as hydrocarbons, halogenated hydrocarbons, aromatics containing no amine, thiol or hydroxyl groups, ethers, petroleum, mineral spirit, cyclohexane or toluene, and, in the cold (approximately 0 to 10xc2x0 C.), water.
Particularly suitable bases are substances containing a tertiary nitrogen, such as triethylamine, dimethylbenzylamine or pyridine. Particularly suitable solvents for the second step of the polymer synthesis are xcex3-butyrolactone, acetone, ethyl acetate, halogenated hydrocarbons, aromatics containing no amine, thiol, or hydroxyl groups, or mixtures thereof. Suitable reaction temperatures are from xe2x88x9210xc2x0 C. to 30xc2x0 C., preferably from 0xc2x0 C. to 20xc2x0 C.
Instead of the precipitation mentioned the solvent may also be removed, in which case the temperature ought not to exceed 60xc2x0 C.
The precipitated polymer is already suitable for use following filtration and drying.
The second reaction step may also take place by means of a phase transfer catalysis in water and an appropriate solvent, e.g., ethers, ethyl acetate, toluene, methylene chloride or chloroform, using cyanogen bromide and triethylamine as auxiliary base at from 0xc2x0 C. to 20xc2x0 C. to give the polybenzoxazole cyanate.
Given below is another preferred reaction scheme for preparing the compounds of the invention: 
Here, the reaction in the first reaction step takes place preferably in methanesulfonic acid with 7% phosphorus pentoxide at 80-140xc2x0 C. for from about 4 to 12 hours. Instead of the acetyl group the hydroxy carboxylic acid may also have been provided with another protective group. A protective alkylcarboxyl group, such as the acetyl group, is subsequently eliminated in dimethylformamide and ammonia. In the case of a protective alkyl group, elimination takes place by means of a strong acid such as hydrobromic acid, for example. The reaction product, a phenyl-linked polybenzoxazole having terminal, aryl- or heteroaryl-attached hydroxyl groups, is subsequently reacted to the end product, a phenyl-linked polybenzoxazole having terminal, aryl- or heteroaryl-attached cyanate groups, with BrCN in an aprotic solvent in the presence of triethylamine.
The polymers of the invention are readily soluble in many organic solvents, examples being acetone, cyclohexanone, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, N-methylpyrrolidone, xcex3-butyrolactone, ethyl lactate, tetrahydrofuran, and ethyl acetate. The polybenzoxazoles of the invention are preferably in a concentration of 5-35% by weight, more preferably 15-30% by weight, based on the overall composition, the solvent in a concentration of 65-95% by weight, more preferably 70-85% by weight. The viscosity of the polymer solution can be controlled by varying the dissolved mass of polybenzoxazole cyanate.
The solution of polybenzoxazole cyanates of the invention and organic solvents may further contain, based on the overall composition, preferably 0.1-15% by weight, more preferably 0.5-10% by weight, of a crosslinker. Through the use of crosslinkers it is possible to exert a positive influence on the cure behavior, the adhesive properties, the strength, and also the thermal and chemical stability of the polybenzoxazole cyanurates. As crosslinkers in this case it is possible preferably to use short-chain compounds containing at least two cyanurate groups. Examples are indicated in the formulae below. These crosslinkers may be added to the polymer solution preferably at from 0.1 to 15% by weight based on the overall composition. With preference it is possible in accordance with the invention to use the following compounds as crosslinkers: 
where R1, R2, R3, and Q are as defined above.
In accordance with the invention the crosslinking reaction proceeds preferably in accordance with the following scheme, to produce polybenzoxazole cyanurates: 
The crosslinking of the polybenzoxazole cyanates to give the polybenzoxazole cyanurates takes place preferably under the action of temperature, more preferably at from 200xc2x0 C. to 400xc2x0 C., but may also take place by means of laser treatment, ultrasound or microwave treatment.
The polybenzoxazole cyanates of the present invention can be used with preference for adhesive bonding. A further-preferred use is their use as dielectrics in electronic components, especially as dielectrics for filling trenches, the trenches having an aspect ratio (ratio of feature height to feature width) of more than 4, with the width of the trenches being only 100 nm or less. When used as adhesives, the polybenzoxazole cyanates of the present invention can in principle be used by the following general method:
a. the polybenzoxazole cyanates of the general formula (I) are applied to the faces of the materials or components to be bonded;
b. the faces to be bonded are brought into contact with one another;
c. the polybenzoxazole cyanates are crosslinked to polybenzoxazole cyanurates.
The crosslinking of the polybenzoxazole cyanates takes place preferably under the action of temperature, that may also take place by means of laser treatment, ultrasound or microwave treatment.
When used as dielectrics, the polybenzoxazole cyanates of the present invention are applied to the substrate to be coated and then crosslinked to polybenzoxazole cyanurates. Thermal crosslinking takes place preferably at a temperature of 200xc2x0 C.-400xc2x0 C., more preferably 250-350xc2x0 C.
Application to the particular substrate, both in the context of adhesive bonding and in the context of function as a dielectric, takes place preferably by applying the polybenzoxazole cyanates in the form of a powder to the face(s) and converting the powder, by heating, into a melt, which can be distributed over the surface, by spreading or brushing, for example.
In a further preferred embodiment, the polybenzoxazole cyanates of the present invention can be applied in a melt or in solution in an organic solvent to the area to be bonded or to be coated, this application taking place by means of spin coating, spraying or spreading or brushing. In this case of solventborne systems, drying is advantageous and in many cases is also necessary. After crosslinking, the polymers of the present invention have a high temperature stability, evident in a thermogravimetric analysis  greater than 450xc2x0 C.
It being a particular advantage of the present invention that no cleavage products are formed or liberated in the course of crosslinking. As a result, the products are particularly suitable for filling very narrow trenches, especially those having an aspect ratio  greater than 4 and trench widths of 100 nm or less.
The polymers of the invention are stable toward process chemicals, such as solvents, strippers, bases, acids or aggressive gases.
A further particular advantage of the materials is the very high bond strength to different surfaces, such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, steel, brass, palladium, silver, tin, tantalum, tungsten, platinum, gold, lead, carbon, including plasma-deposited carbon-containing layers, carbon fibers, silicon or germanium, for example. The polybenzoxazole cyanurates of the invention can therefore be used with preference for the adhesive bonding, for the filling of narrow trenches or features and/or for the coating of these materials.
Further-preferred materials for coating, for the filling of trenches or features or for adhesive bonding are alloys of the abovementioned material or compounds of the above-mentioned materials with oxygen and/or nitrogen, especially silicon carbide, silicon nitride, silicon oxide, titanium nitride, tantalum nitride, silicon oxynitride, tungsten nitride, gallium arsenide, gallium nitride, gallium indium phosphite, indium-tin oxide. In principle, the invention further envisages as being preferred for adhesive bonding those compounds which are employed in microelectronics and optoelectronics, especially chips and/or wafers.
Materials which are further suitable in accordance with the invention for adhesive bonding or coating are ceramics, glass ceramics, glasses, clayware, porcelain, stoneware and/or silicates. For glasses it is possible with preference to use quartz, soda, potassium, soda-potassium-lime, boron-alumina, borosilicate, and potassium lead glasses. Enamel as well can be bonded in accordance with the invention. Moreover, various minerals, such as marble, basalt, limestone, granite, and concrete can be coated and/or bonded with preference in accordance with the invention.
In the case of adhesive bonding, all of the above-mentioned materials can be bonded to themselves or to other of the abovementioned materials.
In the text below the present invention is illustrated with reference to examples, which are not intended to restrict the scope of the invention.